Academic journal article Childhood Obesity

Using Propensity Score Methods to Assess Causal Effects of Mothers' Dieting Behavior on Daughters' Early Dieting Behavior

Academic journal article Childhood Obesity

Using Propensity Score Methods to Assess Causal Effects of Mothers' Dieting Behavior on Daughters' Early Dieting Behavior

Article excerpt

[Author Affiliation]

Donna L. Coffman. 1 The Methodology Center, The Pennsylvania State University, University Park, PA.

Katherine N. Balantekin. 2 Department of Psychiatry, Washington University School of Medicine, St. Louis, MO.

Jennifer S. Savage. 3 Center for Childhood Obesity Research, The Pennsylvania State University, University Park, PA.

*

Current Affiliation: Department of Epidemiology and Biostatistics, Temple University, Philadelphia, PA.

Address correspondence to: Donna L. Coffman, PhD, Department of Epidemiology and Biostatistics, Temple University, 1301 Cecil B. Moore Avenue, Ritter Annex, 9th Floor, Philadelphia, PA 19122, E-mail: dcoffman@temple.edu

Introduction

Dieting to maintain or lose weight is prevalent among both normal weight and overweight female children1,2 and adolescents3 ; estimates suggest that one-third of preadolescent children report dieting.4 There is some evidence that early self-initiated dieting attempts increase the likelihood of disordered eating,5 depressive symptoms,6 overeating, and greater weight gain over time.7-10 The emergence of daughters' dieting has been associated with maternal dieting (i.e., modeling),11 parental encouragement to diet,4,11 and the use of controlling feeding practices such as restriction.12 Both restriction13 and encouragement to diet have been shown to lead to weight gain over time in children,4 suggesting that these practices may be counterproductive. Thus, understanding the emergence of early self-initiated dieting has important implications for public health and obesity prevention and can be used to design interventions to prevent unhealthy eating behaviors and excess weight gain.

A randomized controlled trial (RCT) would guarantee that daughters randomly assigned to maternal dieting and those who are not, are on average, equivalent (i.e., balanced) on measured and unmeasured confounders (e.g., weight concerns). However, as is often the case, randomization is not possible or ethical. Recent advances in statistical methods and software have provided new tools for strengthening causal effect estimates using observational longitudinal data. These methods use propensity scores: the predicted probability of the exposure given measured confounders.14 Confounders are variables that affect both the exposure and outcome and may bias causal effect estimates if not properly accounted for. Propensity scores balance the distributions of measured confounders such that differences in outcomes between exposed and unexposed individuals with similar propensity scores can be used to estimate the causal effect of the exposure. The primary assumption underlying the use of propensity scores is that all confounders have been measured and included in the propensity model. The more measured confounders that are included in the propensity model, the more plausible the assumption. Thus, when using propensity score methods in an observational study, it is critical to measure as many potential confounders as possible. In addition, if there is an unmeasured confounder that is highly correlated with a measured confounder, including the measured confounder in the propensity model will mitigate the bias of the causal effect estimate to the degree that they are correlated.

This article describes and applies both a propensity score method, inverse propensity weighting (IPW), and a standard regression method using observational longitudinal data from the Early Dieting in Girls study to estimate the effect of mothers' dieting at daughters' age 7 on the emergence of daughters' early dieting, operationally defined as emergence of dieting between ages 7 and 11, and whether this effect varies by daughters' baseline weight status. Based on previous studies,11,15 we expect mothers' dieting to have an effect on daughters' dieting. …

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